The low resolution structure of a soluble lipoprotein system has been done by combining x-ray diffraction and EM methods. From this study on the yolk system form amphibian oocytes, it has been possible to determine the arrangement of subunits in the lipoprotein in addition to identifying several unique structural domains in the lipovitellin component. The experiments proposed for the future are aimed at trying to improve the low resolution map by incorporating x-ray data into the calculation and to locate the lipid binding domain in the three-dimensional model. To this end, electron density matching experimentals and lipid extraction studies will be carried out and new maps recalculated when appropriate. Experiments aimed at determining the molecular structure of mitochondrial malate dehydrogenase will be done first at a resolution of 5 A. The x-ray data from two potential heavy atom derivatives, uranyl acetate and p-hydroxymercuriphenyl sulfonic acid will first be measured. Rotation function studies on the native enzyme will help locate positions of local symmetry in the unit cell. The presence of local symmetry will then be used to help find heavy atom positions in this relatively large unit cell. The molecular structure of mitochondrial malate dehydrogenase will then be carefully compared with the known structure of cytoplasmic malate dehydrogenase.